The prolonged grounding of Boeing’s 787 Dreamliner has forced some airlines to seek alternative arrangements, including renting other planes to fill gaps for the upcoming busy summer travel season.

It’s a sign that some Boeing customers don’t expect a quick fix to the 787’s problems.

Jeff Knittel of airplane leasing company CIT said on Tuesday morning that unnamed airlines are talking to CIT about alternatives to the Dreamliner. He said leasing rates for planes like the Boeing 767 and the Airbus A330 “have remained strong and strengthened slightly.”

Boeing’s newest jet has been grounded for almost two months because of two battery incidents, including a fire. Late Tuesday, Boeing received regulatory approval for a proposed redesign of the battery, but extensive testing must be conducted before the 787 can fly passengers again.

Knittel said interest in other planes has come from a handful of airlines that already have the 787 or were supposed to get it before the summer travel season.

“This is not some feeding frenzy out there,” Knittel said at an aviation finance conference. Airline fleet managers are just being practical, he said.

Boeing has delivered 50 planes to eight airlines. Deliveries are currently halted, but the company is still building the planes and has said it still expects to deliver at least another 60 this year.

For now, airlines are making other plans. Last week, Norwegian Air Shuttle, which was due to receive its first 787s in April and June, said it will lease two Airbus A340s along with flight crews if it doesn’t get its 787s on time.

The replacements will be costly for airlines, because planes like the 767 generally have more seats and are not as fuel efficient as the 787. Many airlines planned to use the 787 specifically on routes where the larger 767 was unlikely to be profitable, such as United’s planned Denver-to-Tokyo flight, which has been postponed. United Continental Holdings Inc. has six 787s.

Boeing has 200 engineers working on a battery fix and has proposed a solution to U.S. and Japanese aviation regulators who are currently reviewing it.

Boeing, regulators, and the airlines that fly the 787 haven’t said when they expect the plane to return to the skies. But Knittel’s comments show that at least some airlines don’t think it will be soon.

“This isn’t about whether this will be resolved but when it will be resolved,” Knittel said.

Knittel still stands behind the 787. His company has 10 of them on order and is expected to get its first at the end of 2014.

“I’d love to be in a position where we could accelerate orders,” he said.